In fact, the black line is the condition with black stripes on the molded product. The key reason is the decomposition reaction of molten resin, and the resin with poor heat resistance and flame retardant grade resin (Note: high temperature flame retardant is easy to extrude) and other materials often have black lines. The method to avoid the occurrence of black lines is to adopt measures such as preventing the resin temperature in the material stream from rising too high and slowing down the injection rate. If the inner cavity of the heating barrel or the groove of the screw is damaged, the resin adhering to the upper side is sufficiently overheated, which is prone to decomposition reaction. In addition, the stagnation of the resin at the check valve also causes the decomposition reaction. Therefore, it is necessary to pay special attention to these aspects for resins with high melt viscosity and resins that easily cause decomposition reactions.
1. Poor gloss
Poor gloss is caused by the lack of gloss of the resin on the surface of the molded product, resulting in a milky white mylonite film, which becomes a so-called haze.
The poor glossiness is mostly caused by the surface condition of the abrasive tool. The profile is poorly polished and the surface of the molded product naturally cannot obtain sufficient glossiness.
When the surface condition of the abrasive is excellent, raising the resin temperature and the temperature of the abrasive can improve the gloss of the surface. Conversely, using too much release agent or vegetable oily release agent will damage the surface gloss of the molded product, so pay attention to their use.
Second, the surface layer falls off
The condition where the surface layer of the molded product becomes mica-shaped and falls off is called surface layer fall-off. The reason for the peeling of the surface layer is incorrect mixing of different types of resins or poor molding standards.
As a specific problem of normal operation, the cleaning work when the materials are replaced is incomplete, or the use of broken recycled materials, the wrong type of resin, etc. are likely to cause the surface layer to fall off, so you need to pay attention to these matters.
In addition, when the resin temperature is particularly low, the interior of the fluid resin will cause a boundary layer, which is the cause of the shedding of the surface layer.